Basal and stimulated TSH serum concentrations in euthyroid thyroid nodule patients

Serum TSH concentrations were determined by a sensitive second generation immunoradiometric (IRMA) assay, basally and 20 min after i.v. injection of 200 micrograms of TRH, in 630 consecutive ambulatory clinically and biochemically euthyroid patients with palpable thyroid nodules. The TSH response was defined as normal when the stimulated TSH values was higher than the basal one by at least 2 microU/ml, as suppressed when the difference between the two TSH values was less than 1 microU/ml and as blunted when this difference was between 1 and 2 microU/ml. The TSH response was normal in 511 patients (81.1%), suppressed in 78 (12.4%) and blunted in 41 cases (6.5%). Nodule patients with suppressed responses showed significantly higher mean age (52.7 vs 45.8 years; p < 0.05) and mean serum concentrations of TT4 (9.32 vs 8.71 micrograms/dl; p < 0.05), TT3 (161 vs 137 ng/dl; p < 0.01) and fT3 (4.94 vs 3.86 pg/ml; p < 0.01) than those with normal TSH secretion. Analysis of the distribution of the different TSH responses in the patients grouped according to basal TSH concentration values showed that 50% of the patient group with basal TSH concentration between > 0.2 and 0.3 microU/ml had normal TSH response to TRH. A normal response occurred in 86.5% of patients with basal TSH between > 0.4 and 0.5 microU/ml and in 95.3% of those with basal TSH between > 0.7 and 0.8 microU/ml. The proportion of normal responses in the patients with basal TSH up to 0.1 microU/ml was 15.7% and that of abnormal responses in those with basal TSH > 1.5 microU/ml was 2.7%.(ABSTRACT TRUNCATED AT 250 WORDS)